Two-cycle engine and cylinder block therefor



o. F. CHRISTNER 3,395,6'29

TWO-CYCLE ENGINE AND CYLINDER BLOCK THEREFOR 3 SheetsSneet 1 Aug. 6,1968 Filed Aug. 17, 1966 Arromvn:

1968 o. F. CHRISTNER 3,395,679

TWO-CYCLE ENGINE AND CYLINDER BLOCK THEREFOR Filed Aug. 17, 1966 3Sheets-Sheet 2 INVENTOR CHRIS THE R 5M ATTORNEV:

6, 1968 o. F. CHRISTNER 3,395,679

TWO-CYCLE ENGINE AND CYLINDER BLOCK THEREFOR Filed Aug. 17, 1966 3Sheets-Sheet 3 4 I INVENT l OVALECHRIS FR BY 4mm ism ,yrrok/vers UniteState 3,395,679 TWO-CYCLE ENGINE AND CYLINDER BLOCK THEREFOR Oval F.Christner, Quincy, Ill., assignor, by mesne assignments, to BrunswickCorporation, Chicago, 11]., a corporation of Delaware Filed Aug. 17,1966, Ser. No. 572,997 9 Claims. (Cl. 12373) ABSTRACT OF THE DISCLOSUREThe cylinder block for a two-cycle engine having two cylinders ormultiples of two cylinders disposed in line or in a bank and firingalternately is provided with scavenging or inlet ports and exhaust portsopening toward opposed sides of the block for each cylinder. The opposedscavenging or inlet ports communicate with a crankcase chamber for thecorresponding cylinder through corresponding transfer passages disposedalong each side of the block. The exhaust ports for each cylinder aredisposed angularly to provide for convergence of the corresponding portsof the respective cylinders into a common exhaust passage opening fromeach side of the block. The scavenging or inlet ports, transferpassages, exhaust ports and exhaust passages respectively are allsymmetrically disposed with respect to a common plane containing thecylinder axes.

This invention relates to two-cycle internal combustion engines havingtwo cylinders or multiples of two cylinders disposed in line or in abank such that the pistons in adjacent cylinders of a given multiplefire alternately.

The invention contemplates an engine having an improved cylinder blockadapted for use with a tuned exhaust system. The cylinder block includespassage means providing for increased induction of fuel mixture into thecrankcase and an arrangement of inlet ports and transfer passagesproviding a more complete scavenging of the cylinders. It is generallyan object of the invention to increase the power output for an engine ofgiven cylinder bore and piston strokes.

The drawings furnished herewith illustrate the best mode for carryingout the invention as presently contemplated and set forth hereinafter.

In the drawings:

FIG. 1 is generally a side elevation of a two-cycle, two cylinder,alternately firing engine in accordance with this invention and is shownmounted on the drive shaft housing of an outboard motor;

FIG. 2 is an enlarged sectional view of the engine of FIG. 1 takengenerally on a plane through the axes of the cylinders;

FIG. 3 is a further enlarged view taken generally on line 33 of FIG. 2and shows the underside of the cylinder block with the pistons removed;

FIG. 4 is an enlarged side elevation of the cylinder block with the headbloc-k secured in place and the adjacent pistons shown in opposedextreme positions;

FIG. 5 is a partial sectional view taken generally on line 55 of FIG. 4;

FIG. 6 is a reduced partial sectional view taken generally on line 66 ofFIG. 4;

FIG. 7 is a partial sectional view taken generally on line 7-7 of FIG.2;

FIG. 8 is a reduced partial sectional view taken generally on line 8-8of FIG. 4; and

FIG. 9 is a sectional view similar to that of FIG. 5 and shows anembodiment wherein curved or arcuate transfer passages are employed.

Referring to the drawings, the engine 1 includes the crankcase 2 whichrotationally supports the vertically dis- 3,395,679 Patented Aug. 6,1968 posed crankshaft 3 in the spaced end bearings 4. The engine 1 ismounted on an outboard motor housing 5, shown only in part, whichencloses the drive shaft 6 con nected to the lower end of crankshaft 3.

Intermediate the crankcase bearings 4 the crankshaft 3 is furthersupported by the combined center bearing and valve unit 7 which dividesthe crankcase 2 into separate upper and lower crankcase chambers 8 and9. The unit 7 includes an internal passage 10 adapted to receive theengine fuel mixture from the carburetor 11 through the crankcase opening12. The passage 10 within unit 7 communicates with the respectivecrankcase chambers 8 and 9 through the ports 13 provided in therespective end walls of unit 7. The flow of fuel mixture through theports 13 from passage 10 into the respective crankcase chambers 8 and 9is controlled by the reed valves 14 and 15 mounted on the outside of therespective end walls of unit 7 within the corresponding chambers 8 and9.

The cylinder block 16 is secured to the crankcase 2 of the engine andincludes the vertically spaced cylinder bores 17 and 18 the forward endsof which open into the corresponding crankcase chambers 8 and 9. Theopposite ends of the cylinders 17 and 18 are closed by the head block 19secured to the cylinder block 16.

The pistons 20 and 21 are disposed for reciprocation within thecorresponding cylinders 17 and 18 and are connected by the rods 22 tothe corresponding crankshaft throws 23 and 24 in crankcase chambers 8and 9 respectively. The crankshaft throws 23 and 24 are diametricallyopposed or spaced circumferentially to typify the engine as alternatelyfiring.

The fuel mixture is directed into the cylinders 17 and 18 by two pairsof symmetrically opposed inlet or scavenging ports 25 and 26 which openinto the respective cylinders. When viewed in the direction of thecylinder axes as best shown in FIG. 6, the pair of opposed ports 25 foreach cylinder are generally aligned with each other along a transverseplane generally normal to the common plane containing the cylinder axesand are adapted to direct the flow of fuel mixture adjacent to the outerwall portion 27 of the respective cylinders. The opposed ports 26 areangularly related and disposed at an angle relative to adjacent ports 25as shown in FIG. 6 to provide that the flow streams issuing therefromare directed to a location intermediate the cylinder axis and wallportion 27 and converge to at least partially intersect with the flowstreams from ports 25. For the engine here under consideration, thedesired flow stream direction was attained when the ports 26 weredisposed at an angle of about 15 to a transverse plane normal to thecommon plane of the cylinder axes as shown by the angle 28 in FIG. 6.The impingement of the opposing flow streams of fuel mixture from theopposed ports 25 and 26 starts the loop for scavenging of the cylinderand the net effect of the directions of these ports should provide thatthe main flow body of the loop will begin at a location generally midwaybetween the cylinder axis and the wall portion 27 of the correspondingcylinder and that the entering flow streams be confined to the outerhalf portion of the cylinder so as not to interfere with the returnportion of the loop which moves downwardly through the inner halfportion of the cylinder. As perhaps shown best in FIG. 5, the ports 25and 26 are directed upwardly at an angle to the cylinder wall to impartto the respective flow strearns an upwardly directed component of forceto direct the scavenging loop upwardly. The desired loop characteristicsare attained when ports 25 and 26 are inclined at an angle ofapproximately 7 /2 relative to a horizontal plane as generally shown bythe angle 29 in FIG. 5.

The respective ports 25 and 26 communicate with the crankcase chambers 8and 9 respectively through corresponding transfer passages 30 and 31which are symmetrically dis-posed in the cylinder block 16 relative tothe common plane of the cylinder axes. As perhaps best shown in FIG. 5,the transfer passages 30 and 31 are inclined inwardly in the directionof the corresponding inlet ports 25 and 26 to minimize the introductionof turbulence in the flow stream of fuel mixture at the transition bendfrom transfer passage to inlet port.

The embodiment of FIG. 9 shows an alternative form of transfer passage32 which is arcuate to minimize the transition bend at the juncture ofthe transfer passage and inlet port. The arcuate transfer passage 32 asformed in the cylinder block 33 is provided with a continuing portion inthe crankcase member 34. In the construction of FIG. 9, the compressedfuel mixture moves outwardly into the transfer passage 32 when thedescending piston uncovers the inlet ports and 26 rather then upwardlyand counter the direction of piston travel as in FIG. 5.

The exhaust products of engine 1 leave the respective cylinders 17 and18 by way of the pair of symmetrically opposed exhaust ports 35 whichopen from the inner half portion of the cylinders. The exhaust ports 35are disposed at an angle relative to the cylinders to provide forconvergence of exhaust ports from the respective cylinders on each sideof block 16 into passages 36 which open from the respective sides of theblock.

When the engine 1 is operated with a. tuned exhaust system an exhaustdiffuser or megaphone 37 is secured on each side of block 16 incommunication with the respective passages 36. The tuned exhaustmegaphones 37 are supported from the sides of block 16 by a mountingplate 38 which serves also as a closure for coolant passages 39 and theouter open ends of the fuel mixture inlet ports 25 and 26.

To assure maximum induction of fuel mixture into the crankcase chambers8 and 9 commensurate with the power capabilities of engine 1, additionalinduction facility is provided in the form of a pair of symmetricallyopposed, piston controlled induction ports 40 which open into each ofthe cylinders 17 and 18. The ports 40 are disposed angularly relative tothe cylinders similarly as the exhaust ports 35, as perhaps best shownin FIG. 8.

The induction ports 40 for the respective cylinders 17 and 18 convergeon each side of cylinder block 16 into the ducts 41 which open to therespective sides of the block and are closed off by the exhaustmegaphone mounting plates 38.

The ducts 41 which communicate with. the induction ports 40, in turncommunicate with the corresponding induction passages 42 which extenddownwardly within the cylinder block 16 between the respective cylindersand communicate directly with carburetor 11 through the internal passage10 of the combined bearing and valve unit 7. As generally shown in FIG.7, the induction passages 42 are inclined inwardly toward the cylindersto minimize turbulence at the transition bend between the passages andcorresponding ducts 41.

In the operation of engine 1, the fuel mixture is drawn into thecrankcase chamber during the upward induction stroke of thecorresponding piston. The upwardly moving piston gives rise to apressure reduction in the corresponding crankcase chamber and when thepressure differential across the reed valves is adequate to overcomereed tension, the reed flexes to an open position to admit the fuelmixture. The fuel mixture continues to be drawn into the crankcasechamber past the reed valves as the piston continues to move upwardly.When the upwardly moving piston uncovers the induction ports 40 in thecylinder wall, an additional increment of fuel mixture is drawn into thecrankcase chamber directly from carburetor 11 through the internalpassage 10 of valve unit 7 and the induction passages 42 to supplementthe induction flow past the reed valves and thereby further pack thecrankcase chamber to increase the volumetric efficiency of the crankcaseinduction cycle. In the early portion of the downward or power stroke ofthe piston, the ports 40 are again covered and the pressure in thecrankcase chamber increases to reduce the pressure differential acrossthe reed valves. When the reed tension is able to overcome the reducingpressure differential, the reed valves close.

Following closure of the reed valves and the induction ports 40, thefuel mixture in the packed crankcase chamber is compressed by the pistonas the piston continues to move downwardly on the power stroke. As thepiston approaches the bottom dead center position, the piston uncoversthe inlet or scavenging ports 25 and 26 allowing the compressed fuelmixture to fiow from the crankcase chamber via the symmetrical routesthrough the transfer passages 30 and 31 into the cylinder ahead of thepiston.

The fresh charge of fuel mixture entering the cylinder ahead of thepiston courses the cylinder in a scavenging loop, as generally shown bythe flow arrows in FIG. 2, moving first upwardly in the outer halfportion of the cylinder, then across the top of the cylinder adjacent tothe head block 19, and finally downwardly toward the piston in the innerhalf portion of the cylinder, whereby to scavenge or force out anyremaining combustion products from the previous explosion.

When the piston moves upwardly within the cylinder on its inductionstroke, the piston covers first the inlet ports and then the exhaustports and then proceeds to compress the fresh charge of fuel mixture.Meanwhile the crankcase chamber is being refilled as hereinbeforedescribed. The compressed fuel mixture in the cylinder is ignited justbefore the piston reaches the top of its stroke and the resultingexplosion within the cylinder drives the piston downwardly.

As the piston moves downwardly within the cylinder on its power stroke,the new charge of fuel mixture in the crankcase chamber is beingcompressed as previously described. As the piston approaches the bottomof its stroke, the exhaust ports 35 are uncovered by the piston and thespent charge still under considerable pressure leaves the cylinder.

When exhaust megaphones 37 of proper dimension are employed, the exhaustflow from the cylinder results in a powerful pressure wave which movesthrough the megaphones. This pressure wave is reflected at the open endof the megaphones as a train of suction waves which return to thecylinder. Since the inlet or scavenging ports 25 and 26 are uncovered bythe piston immediately following the opening of the exhaust ports, it islikely that the reflected suction waves materially assist the scavengingloop in the scavenging of the cylinder. Since the engine 1 isalternately firing, the events in the respective cylinders will resultin two power strokes for each revolution of the crankshaft 3.

The cylinder block of this invention with its symmetrically disposedports and passages lends itself readily to accepted manufacturingoperations. The blocks may be cast with cored passages and the portsadded by standard machining practices. While the invention was describedin connection with a two cylinder engine, it is equally applicable tolarger engines having multiples of two cylinders disposed either in lineor in bank wherein the pistons in adjacent cylinders of a given multiplemove oppositely and are alternately fired. With its supplementalinduction capacity, its good breathing characteristics relative toscavenging and exhaust as provided by the symmetrically disposed portsand passages, and when outfitted with a properly tuned exhaust system,the engine of this invention was found to deliver over 30% more powerover an engine of generally similar size and without any increase incylinder bore or piston stroke.

Various modes of carrying out the invention are contemplated as beingwithin the scope of the following claims particularly pointing out anddistinctly claiming the subject matter which is regarded as theinvention.

I claim:

1. In a cylinder block for a two-cycle internal combustion engine withsaid block having at least one multiple of two cylinders adapted to firealternately, said block further containing at least a pair of inlet andexhaust ports respectively for each cylinder, said inlet and exhaustports respectively for each cylinder opening toward opposed sides of thecylinder block and disposed symmetrically with respect to a common planecontaining the cylinder axes.

2. The invention as set forth in claim 1 wherein said block furthercontains transfer passages communicating with said inlet ports andexhaust passages communicating with said exhaust ports, said transferand exhaust passages respectively being disposed symmetrically withrespect to the common plane containing the cylinder axes.

3. The invention as set forth in claim 2 wherein said block is securedto a crankcase having a precompression chamber corresponding to eachcylinder and opening into the adjacent portion of said cylinder, andsaid block fur ther contains induction ports opening into each cylinderfor communication with said precompression chamber and inductionpassages communicating with said induction ports, said induction portsand induction passages respectively being disposed symmetrically withrespect to the common plane containing the cylinder axes.

4. In a two-cycle internal combustion engine, a cylinder blockcontaining at least one multiple of two cylinders adapted to firealternately, the adjacent portions of each said cylinder having a pairof exhaust ports opening toward opposed sides of the cylinder block,said exhaust ports of each cylinder being angularly disposed withrespect to the corresponding side of the cylinder block to provide forconvergence of the corresponding ports of the respective cylinders intoa common exhaust passage opening from each side of the block.

5. The invention as set forth in claim 4 wherein the engine is adaptedfor a tuned exhaust system and an exhaust diffuser communicates witheach of the exhaust passages.

6. In a two-cycle internal combustion engine having at least Onemultiple of two cylinders, a crankcase rotatably carrying a crankshaftand having chambers corresponding to the cylinders, a cylinder blocksecured to the crankcase and containing said cylinders with thecylinders opening into the corresponding crankcase chambers, a pistonreciprocally disposed in each cylinder and connected to the crankshaftin the corresponding crankcase chamber, the pistons in the respectivecylinders moving in opposition to each other to provide for alternatefiring of the cylinders, a carburetor, induction valve means openinginto the respective crankcase chambers and communicating with thecarburetor to supply a fuel mixture for precompression within saidchambers, said cylinder block having scavenging ports opening towardopposed sides of the block for each cylinder and transfer passagesplacing the scavenging ports in communication with the correspondingcrankcase chambers, said cylinder block further containing a pair ofexhaust ports opening toward opposed sides of the block for eachcylinder, the exhaust ports of each cylinder being angularly related toprovide for convergence of the corresponding ports of the respectivecylinders into a common exhaust passage opening from each side of thecylinder block, said scavenging ports, transfer passages, exhaust portsand exhaust passages respectively being symmetrically dispose-d withrespect to a common plane containing the cylinder axes.

7. The invention as set forth in claim 6 wherein the cylinder blockfurther contains induction ports opening toward opposed sides of theblock for each cylinder, said induction ports for each cylinder beingangularly disposed with respect to the corresponding side of thecylinder block to provide for convergence of the corresponding inductionports of the respective cylinders into a common duct on each side of theblock, said ducts communicating directly with the carburetor throughinduction passages provided on each side of the block, said inductionports, ducts and passages respectively being symmetrically disposed withrespect to a common plane containing the cylinder axes.

8. The invention as set forth in claim 6 wherein the symmetricallydisposed transfer passages are arcuate to minimize turbulence at thetransition bend between said passages and the corresponding scavengingports.

9. The invention as set forth in claim 2 wherein the inlet ports aredisposed on an angle with respect to a plane normal to the cylinder axisto provide the flow stream into the cylinder with a component of forcetoward the outer end of the cylinder, and the transfer passage for eachsaid inlet port is inclined toward the cylinder wall in the direction ofthe flow stream.

References Cited UNITED STATES PATENTS 857,120 6/ 1907 Stewart.2,106,427 1/ 1938 Hansson -32 2,406,404 8/ 1946 Ryde. 2,729,204 1/ 6Meyer.

FOREIGN PATENTS 450,396 7/1936 Great Britain. 1,120,317 4/1956 France.

910,002 4/ 1954 Germany.

WENDELL E. BURNS, Primary Examiner.

